Magnetic control system



Nov. 29, 1960 R E ET AL 2,962,601

MAGNETIC CONTROL SYSTEM Filed Aug. 10, 1955 MP iri PM 55 J sou/ms i am wma/v X a 106 06' we:

BL OCK/IVG P0185 SOUR C E BLOC/Y/AG was 145/ SOURCE f6 61 7 SECOND 55 PULSE sol/RC5 SDI/RC5 6 INVENTORS. 5 ARTHUR N. In: &

R57 SECO/VD 5/6 HEWITT D. CRANE s/a/wu azwc: Z [67, 4, DfV/C' Y A TTORNE United States Patent Ofiiice 2,962,601 Patented Nov. 29,

MAGNETIC CONTROL SYSTEM Hewitt David Crane, Princeton, and Arthur W. Lo, Elizabeth, N.J., assignors to Radio Corporation of America, a corporation of Delaware Filed Aug. 10, 1955, 'Ser. No. 527,493

9 Claims. (Cl. 307-88) This invention relates to magnetic systems, and particularly to systems useful in controlling or switching electric signals. In a copending application entitled Magnetic System, Serial No. 455,725, filed by Jan A. Rajchman and Arthur W. Lo on September 13, 1954, there is described a transfluxor. A transfluxor is useful, for example, in the control or the switching of electric signals.

Briefly, a tranfluxor includes a body of magnetic material having a rectangular hysteresis loop and having a plurality of flux paths provided therein. A selected one of the flux paths has at least two portions each, respectively, in common with two other non-selected flux paths. By applying suitable excitation currents to windings linked to non-selected paths, the two common portions of the selected paths can be set to the same or to opposite states of saturation.

An A.C. (alternating current) signal is applied to a signal winding linking the selected path. When the two common portions are in the same state of saturation, an output signal is induced in an output winding linking the selected path. When the two common portions are in opposite states of saturation, no signal is induced in the output winding. Thus, in such an arrangement, a transfluxor can be considered to have two magnetic response conditions, namely, unblocked and blocked response conditions. The transfluxor remembers the response condition to which it is set for an indefinitely long period of time. No holding power is required.

It is a primary object of the present invention to provide an improved magnetic control system employing a transfluxor and an improved method of operation thereof, whereby to enhance the usefulness of such systems.

Still another object of the present invention is to provide an improved magnetic control system having multiple flux paths which are substantially decoupled from each other under one response condition.

A further object of the present invention is to provide an improved magnetic system having a plurality of fiux paths so arranged that successive opposite polarity magnetizing forces can be applied to one flux path, wherein only the first of these magnetizing forces produces a flux change in another of the flux paths having a portion common to the one flux path.

Yet another object of the present invention is to provide an improved magnetic system having a plurality of fiux paths so arranged that signals can be propagated in either direction by actuating either one of two difierent flux paths.

The above and further objects of the present invention are carried out by providing a plurality of apertures including a blocking aperture, a setting aperture and an output aperture so arranged in magnetic material having a rectangular hysteresis loop that all setting signals subsequent to a first setting pulse are confined to a path about the setting aperture which does not enclose the other apertures. The selected path is the one taken about the ouput aperture. By applying a suitable excitation to a blocking winding, the individual paths about the setting and the blocking apertures each has portions saturated in opposite senses, with respect to these apertures, corresponding to a blocked response condition. By applying a signal of one polarity to a setting winding, the portions of the paths about the output and the setting apertures are placed in the same sense of saturation, each path with respect to its own aperture, corresponding to an unblocked response condition. Setting signals thereafter applied to a setting winding, while the transfluxor is in this unblocked response condition, produce flux changes only in the path about the setting aperture. Likewise, A.C. signals applied to an input winding produce flux changes only in the path about the output aperture. The two individual flux paths are therefore substantially decoupled from each other. A new pulse applied to the blocking winding again returns the system to a blocked response condition.

The features of this invention, as well as the invention itself, both as to its organization and method of operation, will best be understood from the following description, when read in connection with the accompanying drawing, wherein like reference numerals refer to like parts, and in which:

Fig. 1 is a schematic diagram of a magnetic system according to the invention, employing a transfluxor having an individual setting aperture and an individual output aperture located in the magnetic material about the blocking aperture;

Fig. 2 is a cross-sectional view along the line 2-2 of the transfluxor of Fig. 1;

Figs. 3a-3c are diagrams useful in explaining the operation of the transfluxor of Fig. l, and

Fig. 4 is a schematic diagram of a magnetic system according to the invention, employing a transfluxor having a setting and an output aperture each position on the horizontal center-line of the transfluxor.

Referring to Fig. 1, a tranfluxor 10 is made from a magnetic material having a rectangular hysteresis loop. The material is in the form of an annular core, and the central aperture 12 of the core is used as a blocking aperture. The material is preferably of uniform thickness, as in the transfluxor 10. A setting aperture 14 and an output aperture 16 are located in the material and have their respective centers located along a horizontal and vertical center-line of the transfluxor 10, as viewed in Fig. 1. The diameter of the blocking aperture 12 is made larger than that of either the setting and the output apertures, for reasons set forth hereinafter. The material between the blocking aperture 12 and the setting aperture 14 forms a leg 1. The material between the setting aperture 14 and the periphery of the transfluxor 10 forms a leg 2. The material between the blocking and the output apertures 12, 16, and the blocking aperture 16 and the periphery of the transfluxor 10, respectively, forms the legs 3 and 4. The cross-sectional areas of the legs taken through their most restricted portions, in the case of legs 3 and 4, for example, conveniently'along a centerline of the transfluxor 10, are equal. The crosssectional area of the most restricted portion of the annular ring, which may be taken, for example, as the leg 5 at the lower portion of the material of the transfluxor 10, is at least equal to the sum of the minimum crosssectional areas of two of the legs adjacent either one of the smaller apertures.

A cross-sectional view of the transfluxor 10 taken along the horizontal center-line 2--2 is shown in Fig. 2. The thickness 1 of the transfluxor 10 may be uniform throughout. A suitable magnetic material having a substantially rectangular hysteresis loop may be, for example, manganese-magnesium ferrite.

A blocking winding 18 is wound through the blocking aperture 12 by threading the blocking winding 18 beginning with the terminal 18a across the top surface (the exposed surface as viewed in Fig. l) of the transfluxor 10, then downwardly through the blocking aperture 12, then along the bottom surface of the transfluxor to the terminal 181;. The terminals of the blocking winding 18 are connected to a blocking pulse source 20. A setting winding 24 is wound through the setting aperture 14 by threading the setting winding beginning with the terminal 24b across the top surface of the transfluxor 10, then downwardly through the setting aperture 14, thence along the bottom surface of the transfluxor It) to the terminal 24a. The terminals of the setting winding 24 are connected to a setting pulse source 26. An input winding 28 and an output winding 30 are wound through the output aperture 16 by threading these windings beginning with their respective terminals'28a and 39a across the top surface of the transfiuxor 10, then downwardly through the output aperture 16, then across the bottom surface to the terminals 28b and 30b, respectively. An input signal source 32 is connected to the terminals 28a and 28b of the input winding 28; and a utilization device 34 is connected to the terminals 30a and 30b of the output winding 30.

A priming winding 36 is wound through both the output aperture 16 and the blocking aperture 12 by thread ing the priming winding beginning with a terminal 36a thereof across the bottom surface of the transfluxor 10, then upwardly through the output aperture 16, then across the top surface of the transfiuxor 10, then downwardly through the blocking aperture 12, and then across the bottom surface of the transfluxor 10 to the terminal 36b. The one terminal 36a of the priming winding 36 may be connected to a priming pulse source 38. The other terminal 36b of the priming winding 36 may be connected to a common conductor, indicated in the drawing by the conventional ground symbol. The priming pulse source 38 is also connected to the common ground.

The various windings are shown herein as single-turn windings for simplicity of drawing; when desired, multiturn windings may be employed. Each of the sources herein are preferably constant current sources such as pentode type vacuum tube circuits.

The positive direction of current flow (conventional) in any source winding is indicated by the arrow adjacent the winding. The blocking pulse source 20 is arranged to furnish a pulse of one polarity, for example, positive, to the blocking winding 18. The setting pulse source 34 is arranged to furnish pairs of pulses comprising a first posi' tive polarity pulse and a second negative polarity pulse to the setting winding 24. The input signal source 32 may be arranged to furnish pairs of pulses; one pulse of the pair is of one polarity and the other pulse of a pair is of the opposite polarity. The priming pulse source 38 is arranged to furnish a positive polarity pulse to the priming winding 26. The utilization device 34 may be any device responsive to the signal induced in the terminals of the output winding 30.

The operation of the system of Fig. 1 will be explained in connection with the diagrams of Figs. 3a through Be. There is an individual flux path about each of the apertures. One of the individual paths, the path 37 about the blocking aperture 12, is shown dotted in Fig. 1. In additron to these individual flux paths, there exists another longer flux path about both the setting aperture 14 and the blocking aperture 12, including the legs 2, 3 and 5.

The conventions regarding the senses of flux flow around a flux path and the corresponding states of saturation of the magnetic material which were adopted in the above-mentioned copending application are retained herein. Briefly, there are two senses of flux flow around a closed path. A positive current flow (conventional) through a surface bounded by the path produces a clockwise (as viewed from that side of the surface into and toward which this current is directed, i.e.,. when facing in this direction of positive current flow) flux around the path linked by the current. This convention conforms to the right-hand rule. One state of saturation, with reference to a closed path, is that in which the saturated flux is oriented in a clockwise sense around the path; and the other state of saturation, with reference to that path, is that in which the saturating flux is oriented in the counter-clockwise sense (as viewed from the same side of the surface) around the closed path.

One manner of operating the system of Fig. 1 is as follows: Assume that the blocking pulse source 20 is operated to cause a positive current pulse 38 to flow in the blocking winding 18. The amplitude of this positive current is made suflicient to establish a clockwise flux saturation throughout each of the legs 1 to 4, inclusive, with reference to the blocking aperture 12. The flux orientation in the respective legs upon the termination of the blocking current is indicated by the arrows of the diagram of Fig. 3a. A pair of arrows is placed in the leg 5 to indicate that the leg contains the sum of the fluxes in the legs 1 and 2 which is equal to the sum of the fluxes in the legs 3 and 4. Note that, with respect to the individual paths about each of the smaller apertures, the flux in either of the two adjacent legs is oriented in opposite senses with respect to the aperture bounded by the two legs.

Each of the windings linked by the changing flux has a voltage induced across its terminals. The windings can be considered to be open-circuited when the blocking pulse is applied, and therefore no current flow is produced by the induced voltage.

Assume, now, that the input signal source 32 is operated to apply a pair of pulses comprising in sequence a negative pulse 40 and a positive pulse 42 to the input winding 28. Neither one of the pair of input pulses produces a flux change in the path about the output aperture 16 because the one or the other of the legs 3 and 4 is already saturated with flux oriented in the direction of the magnetizing force generated by the one or the other of the pair of pulses 40 and 42. Also, the amplitude of the negative pulse 44) is limited, as pointed out more fully hereinafter. Accordingly, the pair of input pulses does not induce any voltage across the terminals of the output winding 30 because no flux change is produced in the path about the output aperture 16.

An indefinite number of pairs of input pulses can be applied without producing any output signals. The amplitude of the negative input pulse 40 is restricted to a value less than that required to generate sufiicient magnetizing force to produce a flux change in the longer path about both the blocking aperture 12 and the output aperture 16, including the legs 1, 4 and 5. The negative pulse tends to produce a flux change from the initial clockwise to the counter-clockwise sense, with reference to the output aperture 16, in these legs. Spurious unblocking of the transfluxor by an input pulse is avoided by so restrict ing the amplitude of the negative input pulse 40. By making the diameter of the blocking aperture 12 much larger than that of the output aperture 16, the permissible amplitude of the negative input pulse 40 can be increased. Note that the amplitude of the positive input pulse 42 can be indefinitely large because each of the legs 1, 4 and 5 is already saturated in the clockwise sense with reference to the output aperture 16.

The transfluxor 10 can be placed in an unblocked condition by operating the setting pulse source 26 to apply a positive setting pulse 44 to the setting winding 24. This positive setting pulse produces a flux change in the legs 3, 2 and 5, from the clockwise to the counter-clockwise sense, with reference to the blocking aperture 12. No flux change is produced in the leg 1 by the setting pulse because the leg 1 is already saturated with flux oriented in the counter-clockwise sense with reference to the setting aperture 14. The flux orientation in the various legs resultingfrom the positive settingv pulse 44 isindicated in Fig. 3b; the dotted arrows indicating the directions of flux which has changed. The blocking pulse source 20 and the priming pulse source 38 may be open-circuited when the setting pulse is applied. Thus, no current flow is produced in the blocking and the priming windings 18 and 36 by the setting pulse.

The flux in the legs 3 and 4 adjacent the output aperture 16 is now oriented in the same clockwise sense, with reference to the output aperture 16, and the transfluxor is unblocked. Pairs of input pulses applied by the input signal source 32 then produce flux changes in the path about the output aperture 16. Each time a flux change is produced a corresponding output signal is induced across the terminals of the output winding 36. Note that the flux orientation in the legs 1 and 2 about the setting aperture 14 is in the same counter-clockwise sense with reference to the setting aperture 14. Accordingly, a succeeding negative setting pulse 46 applied to the setting winding 24 by the setting pulse source 26 produces a flux change in the legs 1 and 2 from the counter-clockwise to the clockwise sense, with reference to the setting aperture 14. The flux configuration in the legs 1 and 2 resulting from the negative setting pulse 46 is indicated in Fig. 3c, the dotted arrows indicating the flux just changed. No flux change is produced in the longer path about the blocking aperture 12 when the negative setting pulse is applied, because all the flux change in the leg 2 is absorbed in the equal and nearby leg 1. Consequently, the negative setting pulse 46 does not induce any voltage in the remaining windings linked to the transfiuxor 10. The flux configuration thus established serves to effectively decouple the setting winding 24, and hence the setting pulse source 26, from the other windings and sources of the transfluxor 10. The initial positive setting pulse 44 can be prevented from producing any current flow in the blocking winding 18 and the priming winding 36 by momentarily inserting a high impedance, or substantially disconnecting these windings by a suitable switch means. For example, a high impedance results momentarily by connecting a suitably poled unilateral conducting device (not shown) in series with the respective windings. The flux orientation in the legs 3 and 4 about the output aperture 16 is still in the same clockwise sense, with reference to the output aperture. Therefore, input signals applied to the input winding 28 still induce corresponding signals in the output winding 30.

The transfluxor 10 can be returned to a blocked response condition by applying a new positive pulse to the blocking winding 18 to return the flux orientation in the respective legs back to the clockwise sense, with reference to the blocking aperture 12. Observe that no flux change is produced in the leg 2 by the second and subsequent blocking pulses because the flux in this leg is already oriented in the clockwise sense with respect to the blocking aperture 12. Therefore, the second and subsequent blocking pulses do not induce any voltage across the terminals of the setting winding 24. The flux orientation in the respective legs following the second blocking pulse is the same as that indicated in the diagram of Fig. 3a. Thus, after any one pair of setting pulses, the setting winding 24 remains decoupled from any of the other windings until after a new blocking pulse 38 is applied; and after the next pair of setting pulses succeeding the new blocking pulse, the setting winding 18 is again decoupled. It is often desirable to incorporate a transfluxor 10 arranged for such decoupling into system applications where interaction between various sources is undesired.

Asymmetrical drive may be used, if desired, by operating the priming pulse source 38 to apply a small amplitude positive priming pulse 48 before each positive input pulse 42. The priming pulse 48 replaces the negative input pulse 40. A relatively large power can be delivered to the utilization device 34 each time the relatively large 6 amplitude pulse 42 is applied. An asymmetrical mode of operating a transfluxor is described in the above-mentioned application, Serial No. 455,725.

The setting and output apertures in the material may be located at various positions about the blocking aperture 12. The angular spacing between the two smaller apertures is not critical. The portion of material separating the smaller apertures should contain sufficient material so that the flux path about the setting aperture is separate from the flux path about the output aperture. The angle of separation may also be enlarged to For example, both small apertures 14' and 16' may be located along the horizontal center-line of an annular core, as shown in Fig. 4, for the transfluxor 10. In the system of Fig. 4, primed reference characters indicate parts similar to those indicated by like, unprimed reference characters of the transfiuxor 10 of Fig. l. The system of Fig. 4, for example, may be used for selectively coupling a first pulse source 56 to a first signal device 60, or a second pulse source 62 to a second signal device 68 by operating one of the signal devices to supply setting pulses. Preferably, only one of the pulse sources is operated at any given time.

Initially, the blocking pulse source 20 is operated to apply a positive blocking pulse to the blocking winding 18', thereby placing the transfiuxor 10' in a blocked response condition. Assume, now, that the first signal device 60 is operated to apply a positive and then a negative setting pulse to a first signal winding 58 wound through the first smaller aperture 14'. The positive setting pulse produces a flux change along the path including the legs 4 and 2 and the transfiuxor 10' is unblocked. The second pulse source 62 is then coupled to the second signal device 68 by means of the flux path about only the second smaller aperture 16. The suc ceeding, negative setting pulse applied by the first signal device 60 produces a flux change only in the path about the first smaller aperture 14'. Thereafter, signals ap plied by the second pulse source 62 to a second input winding 64, wound through the second smaller aperture 16', induce corresponding signals in the second signal winding 66 which is also wound through the second smaller aperture 16'. The first signal winding 58 and the first input winding 59 are decoupled from each of the other windings due to the flux chauge produced in the legs 3 and 4 by the negative setting pulse applied by the first signal device 60.

A second reset pulse applied by the blocking pulse source 20' returns the transfluxor 10' to the blocked response condition. The first pulse source 56 is now coupled to the first signal device 60 by operating the second signal device to apply a positive setting pulse followed by a negative setting pulse to the second signal winding 66. The positive setting pulse produces a flux change along the path including the legs 1 and 3; the succeeding negative setting pulse produces a flux change along the path including the legs 1 and 2. Thereafter, signals applied to the first input winding 59 by the first pulse source 56 induced corresponding signals in the first signal winding 53. The second input and signal windings 64 and 66 are substantially decoupled from the blocking winding 18', and the first input and second signal windings 59 and 58, respectively, due to the counter-clockwise flux orientation in the path about the second smaller aperture 16'. Thus, by employing the pairs of opposite polarity setting pulses, the setting is completely symmetrical with respect to the two smaller apertures.

When the first, smaller aperture 14' is employed as a setting aperture, information is essentially propagated from left to right. That is, when setting pulses are applied to the first signal winding 58, output signals are furnished on the second signal winding 66. When the second, smaller aperture 16 is used as a setting aperture, information is propagated essentially from right to the left. That is, when setting signals are applied to the second signal winding 66, output signals are furnished on the first signal winding 58.

There has been described herein an improved means for decoupling windings linking various flux paths of a transfiuxor by employing means for applying pairs of setting pulses. The setting winding and, consequently, the setting pulse source, is decoupled from any other pulse sources used in operating the transfluxor. The signals applied to the input winding may be pulse type signals, or may be continuous signals such as sinusoidal type signals.

What is claimed is:

1. A magnetic device comprising a core of magnetic material having two remanent states, said core having a central aperture, said core having second and third other apertures therein each through a portion of the core between the inner and outer radial dimensions thereof, said central aperture being located between said second and third apertures, separate first and second winding means wound through said second aperture, a third winding means wound through said third aperture, a first means for producing a magnetic flux in the portions of material on both sides of said central and in the portions of material on both sides of said other apertures in one sense with reference to said central aperture, and means for applying in sequence a first excitation of one polarity and a second excitation of the opposite polarity to said third winding means, said first excitation producing a flux reversal along a path including said third and central apertures, and said second excitation producing a fluxreversal around said third aperture.

2. A magnetic device comprising a core of magnetic material having two remanent states, said core having a central aperture, said core having second and third apertures therein each through a portion of the core between the inner and outer radial dimensions thereof, separate first and second winding means wound through said second aperture, a third winding means wound through said third aperture, means including a winding means wound through said central aperture for producing a magnetic flux in said core portions on both sides of each of said apertures in one sense with reference to said central aperture, and means for applying in sequence a first excitation of one polarity and a second excitation of the opposite polarity to said third winding means, the magnetizing force generated by said first excitation producing a flux change about said central and third apertures, and the magnetizing force generated by said second excitation producing a flux change only about said third aperture.

3. A magnetic device comprising a core of magnetic material having two remanent states, said core having a central aperture, said core having second and third apertures therein each through a portion of the core between the inner and outer radial dimensions thereof, separate first and second windings wound through said second aperture, a third winding wound through said third aperture, a fourth winding wound through said second aperture and said central aperture, a first means for producing a magnetic flux on both sides of said central aperture and on both sides of said second and third apertures in one sense, and means eifective to apply a first excitation of one polarity and a second excitation of the opposite polarity to said third winding.

4. A magnetic device comprising an annularly shaped core of magnetic material having two remanent states, said core having, in addition to its central aperture, second and third apertures therein extending through a portion of the core between the inner and outer radial dimensions thereof, said second and third apertures being so located in the material that the cross-sectional areas at the most restricted portions between the inside surfaces of the respective second and third apertures and the inner and outer radial dimensions of the core are substantially equal, separate first and second winding means wound through said second aperture, a third winding means wound through said third aperture, a first means for producing a magnetic fiux in said cross-sectional areas in one sense, and means effective to apply a first excitation of one polarity and a second excitation of the opposite polarity to said third winding means, said first excitation producing a flux change along one flux path in said core, and said second excitation producing a flux change along another flux path in said core.

5. A magnetic device comprising an annularly shaped core of magnetic material having two remanent states, said core having a central aperture, said core having second and third apertures therein each through a portion of the core between the inner and outer radial dimensions thereof, the inner radial dimension of said central aperture being substantially larger than the radial dimension of any one of said first and second apertures, separate first and second winding means wound through said second aperture, a third winding means wound through said third aperture, a first means for producing a magnetic flux completely around said core in one sense with reference to said central aperture, and means effective to apply in sequence a first excitation of one polarity and a second excitation of the opposite polarity to said third winding means, said first excitation serving to couple said first and second winding means through the magnetic material about said first aperture, and said second excitation serving to substantially decouple said third winding means from any other of the said winding means coupled to said core.

6. A magnetic device comprising a core consisting of substantially rectangular hysteresis loop magnetic material having a central aperture, said core having first and second apertures therein each through a portion of the core between the inner and outer radial dimensions thereof, separate first and second windings wound through said second aperture, a third winding wound through said third aperture, a first means for producing a magnetic flux in the portions of material on both sides of said central and in the portions of material on both sides of said first and second apertures in one sense with reference to said central aperture, means for applying a first excitation of one polarity and a second excitation of the opposite polarity to said third winding, the magnetizing force generated by said first excitation producing a flux change about said central and third apertures, and the magnetizing force generated by said second excitation producing a flux change about said third aperture only, and means for applying alternating polarity input signals to said first winding, said signals causing output signals to be induced in said second winding upon activation of said third Winding.

7. A magnetic device comprising a core of magnetic material having two remanent states, said core having a plurality of apertures therein including a central aperture and second and third apertures, said second and third apertures extending through a portion of the core between the inner and outer radial dimensions thereof, separate first and second winding means Wound through said second aperture, a third winding means exclusively wound through said third aperture, a fourth winding means wound through said second aperture and said central aperture, and means for applying signals alternately in time to said first and fourth winding means, respectively.

8. A magnetic device comprising an annularly shaped core consisting of magnetic material characterized by having a substantially rectangular hysteresis loop having a central aperture, said core having second and third other apertures each through a portion of the core between the inner and outer radial dimensions thereof, separate first and second windings wound through said second aperture, a third winding wound through said third aperture, an additional winding wound through said central aperture, means for applying an excitation of one polarity to said additional winding for producing a magnetic flux in one sense completely around said core, and

means for applying in sequence a pulse of one polarity and a pulse of the opposite polarity to said third winding, said one polarity pulse serving to couple said first and second windings through the magnetic material ad jacent said first aperture, and said opposite polarity pulse serving to decouple said third winding from the other of said windings coupled to said core.

9. A magnetic device comprising a body of magnetic material having a central aperture and second and third other apertures, said other apertures being located in said body adjacent to said central aperture, the material around said central aperture being characterized by having a substantially rectangular hysteresis loop, separate first and second windings wound through said second aperture, a third winding wound through said third aperture, means including an additional winding wound through said central aperture for producing a magnetic flux encompassing said central and other apertures in one sense, with reference to said central aperture, and means for applying in sequence a first excitation of one polarity 10 and a second excitation of the opposite polarity to said third Winding, said first excitation producing a flux change along one flux path in said body, and said second excitation producing a flux change along another flux path in 5 said body.

References Cited in the file of this patent UNITED STATES PATENTS 10 2,284,406 DEntrernont May 26, 1942 2,519,429 Grant Aug. 22, 1950 2,682,632 Cohen June 29, 1954 2,708,219 Carver May 10, 1955 2,802,953 Arsenault Aug. 13, 1957 15 2,820,109 De Witz Jan. 14, 1958 OTHER REFERENCES On the Control of Magnetic Amplifiers," by Ramey, AIEE Technical Paper, 51-389, Sept. 10, 1951 (Figs.

20 2-7, page 10 relied on), pp. 1-11. 

